BANGOR, Maine — The city, in conjunction with the airport, Maine Air National Guard base and numerous other stakeholders, is in the process of implementing a comprehensive watershed management plan designed to improve water quality in Birch Stream.

A meeting was held Thursday outlining that plan, which is being created largely from recommendations by SMRT Inc., a Portland-based environmental engineering firm. SMRT was asked to put together a comprehensive report on the stream that flows off Bangor International Airport after the Maine Department of Environmental Protection deemed the waterway impaired back in 2005.

“This was really a way to help people learn about the issues and start to create a solution,” Wendy Warren, the city’s environmental coordinator, said of Thursday’s meeting. “A lot of that [solution] is dependent on funding and the speed of implementation, but we’re making progress.”

Birch Stream first came under scrutiny in 2003, when DEP officials began investigating contamination of the stream by a de-icing agent the airport was using on military and commercial aircraft. Some residents of the nearby Griffin Park housing complex complained that the propylene glycol antifreeze used in the de-icer caused headaches and other ailments, although there were no scientific data to support those claims.

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DEP did, however, determine that Birch Stream was heavily polluted. But while the airport was certainly partially responsible for the poor quality of the stream — Warren estimated 70 percent — it was hardly the only source. The waterway runs underneath a dense commercial district along Union Street, including the Airport Mall.

BIA and the Air National Guard recently have installed a de-icer collection system, which diverts the fluid from the stream to the city’s wastewater treatment facility. They also have teamed up to clean debris from some sections of the stream.

“We’ve done a significant amount of work, but there is still more to be done,” BIA Director Rebecca Hupp said. “We haven’t developed a timeline.”

Warren said the changes recommended by SMRT for BIA would cost at least $2.5 million, although the airport would not have to shoulder that entire total.

Other businesses and residents in the Birch Stream watershed have expressed concern about the prospect of improving storm-water management, particularly if it means retrofitting their operation.

“Many companies were never required to put in storm-water management plans,” Warren said. “Some have said, ‘What if we do what you’re asking and the stream doesn’t clean up?’ And those concerns are valid.”

Some who attended the Thursday meeting even suggested a moratorium on development, an idea not supported by the city. Warren, however, did indicate that Bangor is considering creating a storm-water management fee system to help pay for maintenance. Other municipalities, including Lewiston, have done so with success, according to Warren.

Because the contaminants found in the stream near Griffin Park are the result of runoff from multiple sources, the DEP cannot force the city into action, but Warren said the city wants to be proactive. With a new watershed management plan in place, the city hopes other sources of hazardous storm water are addressed long before they reach Birch Stream. Warren said it’s important to stress that the watershed management plan is adaptive, or a work in progress.

“We’ll be monitoring it continuously to see what’s working and what’s not,” she said. “It’s not going to happen overnight.”